Eye surgery, and in particular, laser eye surgery procedures such as phototherapeutic keratectomy (PTK), photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and similar refractive procedures, depend heavily on the precise alignment between the eye and a therapeutic (surgical) laser beam. Known techniques for laser eye surgery procedures typically use an ultraviolet or infrared laser to photo-ablate (remove) a microscopic layer of stroma tissue from a cornea to alter its refractive properties. Refractive errors of the eye can thus be corrected by removing a designated portion of the corneal tissue with the laser. Laser ablation procedures can be used to remove targeted portions of the cornea to shape the cornea's contour and correct various conditions, such as myopia, astigmatism, hyperopia and other refractive errors of an eye.
Typical laser eye surgery devices require a patient to be awake during a procedure. This is because a conscious patient can help to improve the outcome of the procedure by maintaining an alignment between his or her eye and the beam of the therapeutic laser. The ability of the patient to maintain such an alignment between his or her eye and the therapeutic laser beam is greatly enhanced by having the patient focus on a target during the procedure.
Such a fixation target can be provided by a commercially available laser light source. Existing commercial laser fixation devices typically use a simple laser beam focused on or near the patient's cornea and rely on the scattered beam image on the cornea to provide alignment These prior art fixation devices use powerful lasers potentially exceeding the limit for a Class 1 laser.
Other prior art fixation devices use a point light source, which expands spatially by the time it reaches a patient's eye. For these devices, separate fixation targets are required for angular and lateral alignment of the eye. Furthermore, the fixation image on the retina becomes blurry due to the patient's refractive (dioptric) errors and the large light bundle that hits the cornea.
Prior art fixation devices, however, have several limitations. The powerful lasers used by prior art fixation systems are, at best, uncomfortable for a patient and, at worst, can damage a patient's retina. This is because the patient fixes his or her gaze on the high power fixation laser throughout the surgery, which causes a very strong stimulus on the macular portion of the retina of the eye undergoing surgery. Thus, although the high power laser provides for the reflection which allows the surgeon to align the patient's visual axis, the potential for permanent eye damage and the lack of patient comfort are of great concern. Furthermore, prior art fixation systems do not provide an effective range of both coarse and fine alignment to allow the patient and the surgeon to easily determine and correct the degree of misalignment between the patient eye and the therapeutic laser beam path.
Therefore, a need exists for a method and system for patient optical fixation that can reduce or eliminate the problems associated with prior art fixation methods and systems. Such a method and system can significantly enhance the ease of use for both the surgeon and the patient via coarse and fine alignment feedback, the use of efficient lower-intensity lasers, and the significantly improved patient fixation, regardless of a patient's dioptric error. A surgeon can thus accurately and efficiently monitor the spatial alignment of a patient's eye, as well as the patient's gaze direction.